While it likely developed as a trade pidgin, Tok Pisin has become a distinct language in its own right. Non-academic Anglophones living in Papua New Guinea tend to refer to it as "Pidgin," "New Guinea Pidgin" or "Pidgin English", but it is common usage among academics, as well as people familiar with Tok Pisin, to refer to the language by its own name.

Between five and six million people use Tok Pisin to some degree, although not all speak it well. Many now learn it as a first language, in particular the children of parents or grandparents who originally spoke different vernaculars (for example, a mother from Madang and a father from Rabaul). Urban families in particular, and those of police and defence force members, often communicate among themselves in Tok Pisin, either never gaining fluency in a vernacular (tok ples), or learning a vernacular as a second (or third) language, after Tok Pisin (and possibly English). Perhaps one million people now use Tok Pisin as a primary language.

Tok is derived from English "talk", but has a wider application, also meaning "word", "speech", or "language". Pisin derives from the English word pidgin; the latter, in turn, may originate in the word business, which is descriptive of the typical development and use of pidgins as inter-ethnic trade languages.

While Tok Pisin's name in the language is Tok Pisin, it is also called New Guinea Pidgin[5] in English. Papua New Guinean anglophones almost invariably refer to Tok Pisin as Pidgin when speaking English.[6] However, professional linguists prefer to use the term Tok Pisin, as this is considered a distinct language in its own right.[7] The language can no longer be considered a pidgin strictly speaking: it is now a first language for numerous people, and is not simply a lingua franca to facilitate communication with speakers of other languages.

This English-based pidgin evolved into Tok Pisin in German New Guinea (where the German-based creole Unserdeutsch was also spoken). It became a widely used lingua franca – and language of interaction between rulers and ruled, and among the ruled themselves who did not share a common vernacular. Tok Pisin and the closely related Bislama in Vanuatu and Pijin in the Solomon Islands, which developed in parallel, have traditionally been treated as varieties of a single Melanesian Pidgin English or "Neo-Melanesian" language. The flourishing of the mainly English-based Tok Pisin in German New Guinea (despite the language of the metropolitan power being German) is to be contrasted with Hiri Motu, the lingua franca of Papua, which was derived not from English but from Motu, the vernacular of the indigenous people of the Port Moresby area.

Along with English and Hiri Motu, Tok Pisin is one of the three official languages of Papua New Guinea. It is frequently the language of debate in the national parliament. Most government documents are produced in English, but public information campaigns are often partially or entirely in Tok Pisin. While English is the main language in the education system, some schools use Tok Pisin in the first three years of elementary education to promote early literacy.

There are considerable variations in vocabulary and grammar in various parts of Papua New Guinea, with distinct dialects in the New Guinea Highlands, the north coast of Papua New Guinea (Pidgin speakers from Finschhafen speak rather quickly and often have difficulty making themselves understood elsewhere) and the New Guinea Islands. The variant spoken on Bougainville and Buka is moderately distinct from that of New Ireland and East New Britain but is much closer to that than it is to the Pijin spoken in the rest of the Solomon Islands.

Tok Pisin, like many pidgins and creoles, has a far simpler phonology than the superstrate language. It has 17 consonants and 5 vowels. However, this varies with the local substrate languages and the level of education of the speaker. The following is the "core" phonemic inventory, common to virtually all varieties of Tok Pisin. More educated speakers, and/or those where the substrate language(s) have larger phoneme inventories, may have as many as 10 distinct vowels.

The verb has a suffix, -im (from "him") to indicate transitivity (luk, look; lukim, see). But some verbs, such as kaikai "eat", can be transitive without it. Tense is indicated by the separate words bai (future) (from "by and by") and bin (past) (from "been"). The present progressive tense is indicated by the word stap – e.g. "eating" is kaikai stap (or this can be seen as having a "food stop").

Adjectives usually take the suffix -pela (now often pronounced -pla, though more so for pronouns, and -pela for adjectives) when modifying nouns; an exception is liklik "little".[8] It is also found on numerals and determiners:

Reduplication is very common in Tok Pisin. Sometimes it is used as a method of derivation; sometimes words just have it. Some words are distinguished only by reduplication: sip "ship", sipsip "sheep".

There are only two proper prepositions: bilong (from "belong"), which means "of" or "for", and long (from "along"), which means everything else. Tok Pisin: "Mipela i bin go long blekmaket". → English: "We went to the black market". Tok Pisin: "Ki bilong yu" → English: "your key" Tok Pisin: "Ol bilong Godons". → English: "They are from Gordon's". (ibid. 640f). Some phrases are used as prepositions, such as long namel (bilong), "in the middle of".

Several of these features derive from the common grammatical norms of Austronesian languages – although usually in a simplified form. Other features, such as word order, are however closer to English.

Sentences which have a 3rd person subject often put the word i just before the verb. This may or may not be written separate from the verb, occasionally written as a prefix. Although the word is thought to be derived from "he" or "is", it is not itself a pronoun or a verb but a grammatical marker used in particular constructions, e.g., "Kar i tambu long hia" is "car forbidden here", i.e., "no parking".

Sign in common use in the 1980s giving a warning in Tok Pisin: "Work on road, cars must stop if you see the red sign."

Tok Pisin is a language that developed out of regional dialects of the languages of the local inhabitants and English, brought into the country when English speakers arrived. There were four phases in the development of Tok Pisin that were laid out by Loreto Todd.

Casual contact between English speakers and local people developed a marginal pidgin

Pidgin English was used between the local people. The language expanded from the users' mother tongue

As the interracial contact increased the vocabulary expanded according to the dominant language.

In areas where English was the official language a depidginization occurred (Todd, 1990)

Tok Pisin is also known as a "mixed" language. This means that it consists of characteristics of different languages. Tok Pisin obtained most of its vocabulary from the English language, i.e., English is its lexifier. The origin of the syntax is a matter of debate. Hymes (Hymes 1971b: 5) claims that the syntax is from the substratum languages, i.e., the languages of the local peoples. (Hymes 1971b: 5). Derek Bickerton's analysis of creoles, on the other hand, claims that the syntax of creoles is imposed on the grammarless pidgin by its first native speakers: the children who grow up exposed to only a pidgin rather than a more developed language such as one of the local languages or English. In this analysis, the original syntax of creoles is in some sense the default grammar humans are born with.

Pidgins are less elaborated than non-Pidgin languages. Their typical characteristics found in Tok Pisin are:

A smaller vocabulary which leads to metaphors to supply lexical units:

Less differentiated phonology: [p] and [f] are not distinguished in Tok Pisin (they are in free variation). The sibilants/s/, /z/, /ʃ/, /ʒ/, /tʃ/, and /dʒ/ are also not distinguished.

All of the English words "fish", "peach", "feast" or "peace" would have been realised in Tok Pisin as pis. In fact the Tok Pisin pis means "fish" (and usually has more of a short "i" sound, almost like the English word "piss", sometimes "pfiss"). English "piss" was reduplicated to keep it distinct: thus pispis means "urine" or "to urinate".

Likewise, sip in Tok Pisin could have represented English "ship", "jib", "jeep", "sieve" or "chief". In fact it means "ship".

belo – bell - as in "belo bilong lotu" = "Church bell". By extension lunch or midday break (from the bell rung to summon diners to the table). A fanciful derivation has been suggested from the "bellows" of horns used by businesses to indicate the beginning of the lunch hour but this seems less likely than the straightforward derivation.

bilong wanem? – why?

buai – "betelnut"

buai pekpek – "betelnut spit"

bubu – grandparent, any elderly relation – also grandchild. Possibly from Hiri Motu – where it is a familiar form of tubu, as in tubuna or tubugu.

kakaruk – chicken (probably onomatapoetic, from the crowing of the rooster)

kamap – arrive, become (from "come up")

kisim – get, take (from "get them")

lotu – church, worship from Fijian, but sometimes sios is used for "church"

mangi/manki – small boy, by extension, young man (Probably from the English jocular/affectionate usage "monkey", applied to mischievous children, although a derivation from the German "männchen", meaning "little man" has also been suggested)

pisin – bird (from "pigeon"). The homophony of this word with the name of the language has led to a limited association between the two; Mian speakers, for example, refer to Tok Pisin as "wan weng", literally "bird language".

susa – sister, though nowadays very commonly supplanted by "sista". Some Tok Pisin speakers use "susa" to indicate a sibling of the opposite gender, while a sibling of the same gender as the speaker is a "brata" or "barata".

susu – milk, breasts, from Malay

tambu – forbidden, from "taboo", but also means "in-laws" (mother-in-law, brother-in-law, etc.) and other relatives whom one is forbidden to speak to, or mention the name of, in some PNG customs.

^The published court reports of Papua New Guinea refer to Tok Pisin as "Pidgin": see for example Schubert v The State [1979] PNGLR 66.

^See the Glottolog entry for Tok Pisin (itself evidence that the linguistic community considers it a language in its own right, and prefers to name it Tok Pisin), as well as numerous references therein.

^Liklik can also be used as an adverb meaning "slightly", as in dispela bikpela liklik ston, "this slightly big stone".